Rumors are swirling that former Massachusetts governor Mitt Romney will pick his vice presidential candidate this week, although Romney adviser Eric Fehrnstrom told reporters Monday that “no decision’s been made.”

Don’t hold your breath.

The Republican National Convention is over a month away, and no non-incumbent candidate has picked a VP so far ahead of his party’s nominating confab. Most picks come within a week of the event.

President Obama chose Sen. Joe Biden as his running mate on the Saturday before the 2008 Democratic National Convention, telling supporters of his pick by text message. Gallup found no bump in polls.

Sen. John McCain (R-Ariz.) announced at a rally a week later that he had tapped Alaska Gov. Sarah Palin, just a few days before the GOP convention.

Sen. John Kerry (D-Mass.) picked Sen. John Edwards (D-N.C.) on July 6, 2004, 20 days before the convention.

“[N]aming Mr. Edwards did not immediately win over any substantial number of voters for the Democratic ticket, and the campaign between Mr. Kerry and President Bush remains statistically deadlocked,” the New York Times said two weeks later.

Texas Gov. George W. Bush chose former Defense Secretary Dick Cheney as his running mate on July 24, 2000, about a week before the Republican convention.

Vice President Al Gore chose Sen. Joe Lieberman (D-Conn.) on Aug. 7, 2000, a week before the Democratic convention.

Four years earlier, Sen. Bob Dole (R-Kansas) chose former Housing Secretary Jack Kemp as his running mate on Aug. 10, two days before the convention.

In 1992, Arkansas Gov. Bill Clinton picked Tennessee Sen. Al Gore on July 10, two days before the convention.

Massachusetts Governor Michael Dukakis picked Sen. Lloyd Bentsen (D-Texas) on July 13, 1988 — five days before the Democratic convention. Vice President George H.W. Bush announced Sen. Dan Quayle (R-Ind.) as his running mate on Aug. 17, 1988 — two days into his party’s convention.

In 1984, former vice president Walter Mondale picked Rep. Geraldine Ferraro (D-N.Y.) as his running mate a few days before the Democratic convention.

Before 1984, nominees were picked at the political conventions, often after some political wrangling over the presidential nominee.

Ronald Reagan chose George H.W. Bush at the 1980 convention, a last-minute shift that caught attendees by surprise. Reagan had been in talks with former president Gerald Ford, but their negotiations reportedly hit a snag over the role of the vice president.

In 1976, President Gerald Ford announced his choice of Dole on the last day of the convention, after winning a floor fight with Reagan. Knowing he would face a challenge from the right, Ford had dropped Vice President Nelson Rockefeller from the ticket the previous fall.

Sen. George McGovern (D-S.D.) chose Sen. Thomas Eagleton (D-Mo.) at the 1972 convention after Sen. Ted Kennedy (D-Mass.) turned him down. After the convention, Eagleton admitted to having undergone electroshock therapy, and McGovern was pressured into replacing him with Peace Corps founder Sargent Shriver.

So, simply put, it would be highly unusual for Romney to pick a running mate so far ahead of his party’s convention. That doesn’t mean the speculation will end, but it’s reason to be very skeptical.